usurpation

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The act of usurping, especially the wrongful seizure of royal sovereignty.
• noun A wrongful seizure or exercise of authority or privilege belonging to another; an encroachment.

from The Century Dictionary.

• noun The act of usurping; the act of seizing or occupying and enjoying the place, power, functions, or property of another without right; especially, the wrongful occupation of a throne: as, the usurpation of supreme power.
• noun In law: Intrusion into an office or assumption of a franchise, whether on account of vacancy or by ousting the incumbent, without any color of title.
• noun Such intrusion or assumption without lawful title.
• noun The absolute ouster and dispossession of the patron of a church by presenting a clerk to a vacant benefice, who is thereupon admitted and instituted; intrusion. Use; usage.

from the GNU version of the Collaborative International Dictionary of English.

• noun The act of usurping, or of seizing and enjoying; an authorized, arbitrary assumption and exercise of power, especially an infringing on the rights of others; specifically, the illegal seizure of sovereign power; -- commonly used with of, also used with on or upon.
• noun obsolete Use; usage; custom.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun The wrongful seizure of something by force, especially of sovereignty or other authority.
• noun Trespass onto another's property without permission.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun wrongfully seizing and holding (an office or powers) by force (especially the seizure of a throne or supreme authority)
• noun entry to another's property without right or permission